In order to cook items, you must have an E-Z Cook Oven™. When you get one, you'll see a link at the top of your inventory that says, conveniently enough, "cook stuff." Click that and you're well on your way to becoming a master chef.

Some items can only be cooked by players of certain classes, or by players with certain skills. Feel free to experiment with various kinds of food items to make tasty meals. Some of the recipes make perfect sense, and some... well... some are specifically designed to be a challenge.

Yeah, that's the ticket.